Downlink Synchronization (DL Sync) is important to 5G applications including, but not limited to, enhanced mobile broadband (eMBB), massive machine type communication (mMTC) and ultra-reliable/low latency (UR/LL). In particular, DL Sync is the provisioning mechanism for symbol, slot and subframe/frame timing for all 5G applications.
Propagation delays are dependent upon the deployment scenario. For example, the maximum propagation delay for outdoor deployment scenarios is 4.0 μs. Meanwhile, the maximum propagation delay for indoor deployment scenarios is about 0.4 μs. However, existing systems, such as 3GPP LTE/LTE-A cells, employ the same cyclic prefix duration regardless of the deployment scenario. Existing systems therefore are undesirable for handling diverse applications.
While 5G systems support various numerologies such as transmission time intervals (TTI)s and subcarrier spacing, protocols for supporting 5G user equipment (UE) to acquire DL symbols, frame timing and cell identification on a cell search stage are unavailable. Based upon current DL Sync designs, the 5G UE cannot blindly detect the supported numerologies.
Separately, the UE needs to perform neighboring cell measurements for cell reselection in a radio resource control (RRC)-idle or RRC-connected state. Reselection requires knowledge of the numerology of the neighbor cell DL sync signals. In 5G systems, however, different DL Sync signal numerology may be used at different cells. Methods are desired to improve neighboring cell measurement in 5G systems.
Applications such as eMBB, mMTC, and UR/LL exhibit different latency and power savings requirements. DL Sync signal design and cell search procedures are needed to support these requirements in 5G systems.
New radio (NR) Access Technology helps identify and develop technology components needed for systems operating at frequencies up to 100 GHz. For example, see 3GPP TR 38.913, Study on Scenarios and Requirements for Next Generation Access Technologies; (Release 14), V0.3.0, as well as RP-161214, Revision of SI: Study on NR Access Technology, NTT DOCOMO. To compensate for the increased path loss in these High Frequency NR (HF-NR) systems, beamforming is expected to be widely used. However, the existing initial access signal design such as DL synchronization, reference signal and PBCH design, which is based on omnidirectional or sector-based transmission, does not support the functions required for beamforming based access (e.g., beam sweeping, beam pairing, beam training, etc.).
Present network access procedures are based on omni-directional transmission or sector-based transmission. For example, this may include cell search procedures and subsequent Physical Broadcast Channel (PBCH) acquisition. However, some functions for beamforming based access are not supported by existing omni-directional or sector-based transmission access procedures. One of these functions includes beamforming pair determination in idle state. Another function includes beamforming training feedback and beamforming training reference signal (BT-RS) transmission, e.g., whether to perform before, during or after RRC Connection setup. Yet another function includes the resources of uplink (UL) channel for beamforming (BF) training feedback in view of time and frequency. A further function includes beamforming based PBCH detection.